This page of the guide to Halo Infinite has a walkthrough of main mission 2 - Foundation. The walkthrough informs, e.g. where to find the Weapon, how to follow the signal, how to reach the passage leading to the surface, and how to defeat the first boss of the game - Tremonius.
Locate the Weapon
Watch out for numerous abysses - falling into one of them will kill you instantly. You should especially watch out during fights, because it is easier to get lost and lose stable ground. Use the Grappleshot to pull yourself towards shelves. Remember to aim accurately.
Soon after the start of the mission, you will again encounter an officer shooting red missiles. Do not stop shooting at him.
The linear route will lead you to the gravity elevator - step into it to move upwards. In the locations with chasms, use the Grappleshot to pull yourself to the shelves. Defeat enemies along the way.
In the location in the image, head towards the interactive station where you will encounter the Weapon - a rebel AI. Press X to place the AI chip in the Master Chief's armor.
Follow the signal
You will have to defeat more enemies. You will reach an inactive bridge generation device to which you need to deliver the Power Seed. Use the scanner and look around the area - the energy source is in the place shown in the image.
Move the large object and place it in the slot of the previous device. Cross the newly created bridge and reach the terminal from which the Weapon can get data.
Reach the surface
Reach the next device for creating a bridge. Expect more battles with regular opponents. The only problem you can encounter is the stationary turret from the picture. You can kill the enemies trying to use the turret if you have a good ranged weapon (optimally a sniper rifle). If you don't have it, use sprint to move from one large cover to the next to safely approach the turret and kill anyone who is using it.
In one of the next rooms, you will encounter an enemy called a Grunt Mule - they always drop a lot of weapons upon death.
Watch out for the first sniper in the next room (image above). You can identify these enemies by their large laser beams. You can either shoot them from a distance (there is, e.g. a Skewer in the area) or get close to them (preferably by using the Grappleshot) and kill.
You must again solve a mini-puzzle - find and deliver a power seed to the inactive console. Using the scanner will allow you to determine that the energy source is on the higher shelf shown in the picture - pull yourself there with the Grappleshot. Using the power seed will unlock a new gravity elevator.
Go forward. On the way, you will pass an impossible-to-miss corpse of a Spartan - you will get a Shield Core - this is an upgrade for the Master Chief's armor that increases the strength of the shield. In the later part of the game, you will also be able to improve the Shield Core to further strengthen the shield.
In the next, you will have to defeat enemies - watch out for enemy snipers. After the fighting, replenish ammunition and grenades and then look for the elevator call button. Once again, you will need to find a power seed. Follow the indicators on the screen to reach the location from the picture and find the energy source. Get it back to the console.
Boss fight - Tremonius
The elevator ride will not go as planned - it will take you to boss Tremonius. He's the first boss of the campaign. We suggest dealing with regular opponents first.
The boss uses a jetpack to move around the area. You should be on the move at all times, even when Tremonius is standing far away from the hero. The enemy can quickly close in on you.
The boss is using a Hydra launcher which can cause serious damage. Move around the area a lot to be a harder target to hit.
Unfortunately, Tremonius has an extra white shield bar, which you have to deplete first. Only after depleting the white shield bar, you can deal real damage to the boss.
To attack the boss, you can use any weapons and grenades. There are some supplies in the vicinity, such as racks that let you switch weapons if you run out of ammo.
Hide behind the covers if Master Chief loses his shield. However, don't take too long breaks between one attack and the next -Tremonius' shield can restore Fortunately, the boss can not regenerate the lost health points.
After the battle, activate the elevator to complete this task and automatically advance to the next.